Engineering Controls Database
Mine Assay Laboratories
| Workers in mine assay laboratories are exposed to respirable dust and silica, lead, arsenic, mercury, and other elements in the ore that is produced from samples that are oven-dried, split, crushed, and pulverized. These emissions also come during fluxing operations where the prepared sample is mixed with lead oxide, borax, flour, silica sand, and soda ash. | |
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Lead targets four major organs and systems: the central nervous system, the peripheral nervous system, kidney, and the hematopoietic (blood-forming) system. Inhalation or ingestion of inorganic lead can cause a range of symptoms and signs including loss of appetite, metallic taste in the mouth, constipation, nausea, colic, pallor, a blue line on the gums, malaise, weakness, insomnia, headache, irritability, muscle and joint pains, fine tremors, and encephalopathy. Lead exposure can result in a weakness in the muscles known as “wrist drop,” anemia, proximal kidney tubule damage, and chronic kidney disease. Lead exposure is associated with fetal damage in pregnant women. Finally, elevated blood pressure has been positively related to blood lead levels. Crystalline silica causes silicosis, a form of disabling, progressive and sometimes fatal pulmonary fibrosis characterized by the presence of typical nodulation in the lungs or chest X-ray. Historically, many silicotic workers had tuberculosis. In some mines up to 60 percent of the workers with silicosis had tuberculosis. Evidence indicates that crystalline silica is a potential occupational carcinogen. Inorganic arsenic is strongly implicated in respiratory tract and skin cancer and has been determined to be a potential occupational carcinogen by NIOSH. Inorganic arsenic has caused peripheral nerve inflammation and degeneration, anemia, reduced peripheral circulation, and increased mortality due to cardiovascular failure in workers who have been exposed to inorganic arsenic through inhalation, ingestion, or dermal exposure. Acute effects of overexposure to inorganic mercury include chest pain, cough, chemical pneumonitis and bronchitis. Chronic exposures can produce symptoms of weakness, loss of appetite, loss of weight, insomnia, diarrhea, nausea, headache, and excessive salivation. It may also cause metallic taste in the mouth, loose teeth, soreness of the mouth, a black gum line, irritability, loss of memory, and tremors of the hands, eyelids, lips, tongue, or jaw. Three historical manifestations of mercury poisoning are: gingivitis, increased irritability, and muscular tremors. Mercury can cause allergenic skin rash and is a primary irritant of the skin and mucous membranes. |
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All of the mines examined by NIOSH employ local exhaust ventilation and partial enclosures in the sample preparation area, flux mixing, and fire assay areas.. In the sample preparation laboratory the sample splitter hood, cone crusher and jaw crusher are equipped with downdraft local exhaust ventilation. Flexible hoses from the three units connect into a distribution box which is tied into a single exhaust fan. Each pulverizer has its own ventilated hood with a glass door in front. The sash of the glass door is positioned 4 inches above the bench so that make-up air flows under the door into the hood. The glass door prevents dust from being blown into the room while the pulverizer is being cleaned with compressed air. Next to both pulverizer hoods are pouring stations with ventilated hoods. Each hood has a 2 HP fan with a 1725 rpm motor. The air from these systems is either filtered and recirculated or it is exhausted directly outside. In the fire assay area premixed flux including lead oxide, silica sand, and other ingredients are mixed in an exhaust hood made of plexiglass with the exhaust opening in the table. The premixed flux contains a mineral oil which helps control dust levels – especially lead – during mixing. There is also an automatic mixer that is sometimes used to mix the flux with the samples which helps reduce the workers exposure compared to hand mixing. Each of the fusion furnaces has an exhaust hood on top of the furnace above the door. The primary purpose of these hoods is to exhaust fumes when the doors are open. The cupellation furnace has a large hood that is above the furnace. Exhaust air from these local exhaust ventilation units is discharged directly outside.    |
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| 198-11A; 198-11B; 198-12A; 198-13A; 198-14A; 198-14B; | |
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deposit mapping lab workers mine assay lab workers mine assay laboratories mine lab mineral exploration mineral lab mineral ore |